Adhesive and coating composition



Patented Got. 20, 1936 UEE STATES PATENT OFFICE ADHESIVE AND COATINGCOMPOSITION Harry L. Fisher, Leonia, N. J assignor, by mesneassignments, to United States Rubber Com.- pany, New York, N. Y., acorporation of New This invention relates to an adhesive and coatingcomposition, and more particularly to a composition especially adaptedfor uniting rubber to metal or for coating metallic and other articles.

In the chemical and other arts there has been difficulty in themanufacture of suitable containers and shipping receptacles for variouscorrosive liquids and other materials. In some cases the containers aremade of glass or other material unattackecl by the corrosive liquids,but in the case of glass the material is quite fragile and unsuited forlarge receptacles or for transportation purposes, and many of the otherexpedients used are too expensive. As a result attempts have been madeto use receptacles and tank cars made of steel or iron and to line themwith rubber, but difliculty has been encountered in obtaining a bondbetween the rubber and metal which is at the same time strong andunafiected by conditions met during use, such as high temperatures, andwhich is also economical to produce and simple to make.

A further use in the arts for composite rubber and metal articles is incases where the articles are exposed to corrosive gases, such as partsof blower or exhaust systems, and in cases where metal is lined withrubber to prevent abrasion of the metal, as in rubber lined metal chutesand in conveyor buckets and various other parts of conveying systemshandling abrasive materials. Furthermore it is desirable to providestrong adhesion between rubber and metal parts in the manufacture ofvibration-absorbing engine mountings and the like.

One method of uniting rubber to iron or steel is to plate the metal withbrass, apply a cement of unvulcanized rubber compounded to form hard'rubber, dry, and then superpose the rubber lining and vulcanize. Thismethod is not of general application, is unsuitable for the lining ofreceptacles, and a further objection is that a relatively long time andhigh temperature are required to moplastic softens under heat attemperatures as low as 80 C., and the bond isthen weakened.

Hence, this method isnot applicable in the case of receptacles or otherarticles subjected to temperatures higher than about 70 C.

A further difiiculty in the chemical and other arts is to obtain aprotective coating composition applicable to metal, wood, paper andother materials, which is strongly adhesive, flexible and highlyresistant to various chemical reagents.

The present application is a continuation-inpart of my applicationSerial No. 474,298, filed August 9, 1980.

An object of the present invention is to provide an improved adhesivecomposition suitable for uniting rubber and rubber-like materials tometal, and which is also applicable for uniting various other materialssuch as wood, leather, paper, fabric, etc.

A further object is to provide an adhesive composition which afterapplication may be nonthermo-plastic and hence will not tend to softenand weaken the joint in a composite article when the latter is subjectedto high temperatures.

A further object is to provide an adhesive composition which iseconomical and simple in application.

A still further object is to provide an improved coating composition.

Other objects will appear from the detailed description and claims.

I have discovered that by mixing certain rubber products which inthemselves have little or no bonding strength, and interposing a layerof the resulting composition between bodies of metal and rubber orbetween other bodies which it is desired to adhesively unite, acomposite article is obtained which has all of the desired properties ofgood bonding strength, cheapness and durability. The combination isfurther improved by the addition of certain softening agents and/orvulcanizing ingredients including accelerators. The adhesive is suitablefor uniting such materials as rubber, rubber-like hydrocarbons such asbalata, synthetic rubbers, leather, wood, fabric, paper, metal, glass,etc. and in those cases where a very high bonding strength is notrequired further vulcanization of the adhesive, after its application tothe surfaces to be united, may be dispensed with. The rubber or similarmaterials may be employed in the form of calendered sheet or as thedeposit from a natural or artificial dispersion. In those cases where amaximum bonding strength is desired, and particularly in the union ofmaterials such as rubber and metal, the applied adhesive may bevulcanized in situ with a corresponding increase in strength. This alsorenders the bond non-thermoplastic at temperatures up to at least 120C., which greatly extends its field of usefulness.

hours at 35 pounds steam'pressure. rubber solution thus obtained will behereinafter In one form of the adhesive composition of the invention,there may be prepared a mixture composed of a solution of hard rubber ora rubber of the hard rubber type and a solution of rubber vulcanized toa substantially less degree of combined sulphur. Boththe solution ofhard rubber and the solution of rubber vulcanized to a less degree ofcombined sulphur may be prepared in a manner similar tothat described inpatent to Gibbons et al. No. 1,745,533, issued quire 2%; hours at atemperature of approximately 163 C. The patent also states that lowertemperatures may be used with a correspondingly longer time, and asexamples the solution may be heated forShours at a temperaturecorresponding to pounds steam pressure, or for 48 The hard designatedproduct A. This solution of hard rubber may then be mixed'with a similarsolution the rubber of which has been Vulcanized to a substantially lessdegree of combined sulphur,

usually to 4 to 6% combined sulphur. For instance, there may be used forthe latter'solution the product obtained by heating a solution of softvulcanized rubber with sulphur for 2 hours at 35 pounds steam pressure,which product will hereafter be known as No. 1, or there may' be usedthe product obtained by heating a solution of soft vulcanized rubberwith sulphur for four hours at 35 pounds steam pressure,

which latter product will hereafter be. known as No. 2. If desired, thesolution of hardrub- 'ber may be mixed with a solution ofv softvulcanized rubber, such as that used for'thepreparation of products No.l and No. 2, without the addition of any further sulphur. The solutionof soft vulcanized rubber employed forthepreparation of the furthervulcanized solutions'may be prepared under the time and temperatureconditions specified in the patent to Gibbons et al., that is, byheatingthe soft vulcanized rubb'er, suchas inner tube scrap, in a kettlewith a solvent such as high flash solvent naphtha for two to three hoursat approximately 163 C., or instead it may be prepared by heatingthescrap and solventfor from 16 to 90 hours-at a temperature correspondingto 35 pounds steam pressure. The solution of soft vulcanized rubbercontaining no further added sulphur .willhereafter be referred to asproduct No. 3.

When mixing the solution of hard rubber and the solution of rubbervulcanized to a less degree of combined sulphur, the concentration ofthe solutions may be varied according to conditions, but approximately10 to 25% solids has been found to be suitable in most instances. Thehard rubber solution and the solution of rubber vulcanized to a lessdegree of combined sulphur may be mixed in different proportions, butproportions varying from 8 to 1 down to 1 to 1 of the respectivesulphurized rubber have been found most suitable when bonding rubber tometal, and the composite rubber-metal articles thus obtained have givenstripping pulls up to pounds .per inch and higher. While it ispreferredto use a rubber solution the rubber of which has 15% or morecombined sulphur, as that ingredient of the composition which has thehigher ratio of combined sulphur, the invention is not limited to suchuse, and there may be employed instead a rubber solution which has aless proportion of combined sulphur.

If desired raw or unvulcanized rubber or balata may be included in anyof the above described adhesive compositions, whereby the body of thecomposition, and the tackiness of dried uncured layers depositedtherefrom, are increased, for which purpose any of the usual rawrubbers, such as pale crepe, spray dried rubber, etc. may be used. Anaccelerator of vulcanization with or without additional sulphur andother vulcanizing ingredients such as zinc oxide, may also be included.Also, any one of the described solutions of vulcanized rubber may beincorporated with unvulcanized rubber or rubber-like hydrocarbonmaterial (such as balata), and vulcanizing ingredients, to produce anexcellent adhesive. e

In all the described forms of the invention the composition embodies inpart a rubber-like hydrocarbon material combined with sulphur anddiffering substantially in its combined sulphur content from theremaining rubber-like hydrocarbon material, that is, the remainingmaterial may have less combined sulphur and/or no combined sulphur.

The compositions above described have been found to give very highresistance to separa tion, particularly when further vulcanized in situ.When testing the strength of the bond, for instance between rubber andmetal, a standard method of preparing a sample is to apply a solu; tionof the adhesive composition to a flat plate of cleaned metal, dry, thensuperimpose thereon two layers of a calendered vulcanizable rubbercompound having a fabric reinforcement therebetween of square wovenfabric such as that sometimes used in tire construction, and thenvulcanize the composite material. The fabric insert is used merely toprevent stretching of the rubber during the stripping test and therebyinsures accuracy in the pull figures obtained. In carrying out thestripping test, a strip one inch wide, and extending inwardly from anedge of the composite rubber-metal article, is marked out on therubberized fabric stock and the latter is then cut through on the markedlines to the surfacev of the metal. The one inch wide strip thus formedis loosened at an edge of the composite rubber-metal article, and thestrip end and the metal plate beneath it are fastened respectively inthe lower and upper grips of a standmachine.

The following examples give the results of tests carried out onrubberized fabric-metal articles in which the bonding was accomplishedby the 'use'of theadhesive compositions of the present invention.

Example 1.-Using a mixture of the hard rub ber solution A and the No. 2product before mentioned, in proportions varying from 6 to 1 to ,8 to

1, the pull obtained was between 50 and 52 pounds when an ordinary tiretread stock was used as the cover stock.

. Example 2.-Using a mixture of the hard rub ber solution A and asolution of product No. 1,

previously described, on a tread stock, a pull of 2'7 pounds wasobtained using a 4 to 1 ratio of the solutions; a pull of 26 pounds wasobtained using a 3 to 1 ratio; and a pull of 24 pounds was obtained witha 2 to 1 ratio; while with a '7 to 1 ratio a pull of 42 pounds wasobtained.

Example 3.Using a mixture of the hard rubber solution A and the solutionof soft vulcanized rubber, previously referred to as product No. 3, a 6to 1 mixturewith a tire tread stock gave .a pull of 27 pounds, while a 4to 1 mixture with a tread stock gave a pull of 24 pounds. Using a tirecarcass stock, a 2 to 1 mixture gave 17 pounds pull.

In the above examples, the cure of the composite rubber-metal articlewas in a press, and unless otherwise specified the cure for a treadstock was '75 min. at 40 pounds steam pressure and for a carcass stock60 min. at 40 pounds steam pressure.

If desired, a vulcanized stock may be used instead of a vulcanizable oneand in this case the curing time required to produce a good bond is verymuch lessened under the same temperature conditions.

In applying the bonding mixture to the metal, the latter may be cleanedin any suitable manner as by sand blasting or by the use of a suitablepickle, and the bonding mixture then applied in any suitable way such asby pouring, spraying or spreading. The bonding mixture is thenallowed'to dry and the rubber stock applied and rolled down. While theinvention is particularly applicable to the uniting of rubber to ferrousmetals, such as iron or steel, it has'also given good results with othermetals such as aluminum and brass.

As showing that the bond of the composite article is not affected byhigh temperatures, a test was made using as the bonding material a mixture of the hard rubber solution A and the No. 2 product beforedescribed, and after vulcanizing, the bond between iron and a tire treadstock was excellent under high temperatures. After 16 hours heat at 212F. a pull of 49 pounds was obtained on the composite materialimmediately after it was removed from the oven, and a pull of 50 poundswas obtained when tested cold.

Further improvement is effected by adding to the bonding compositioncertain organic softening agents, among which may be mentioned aniline,dimethylaniline, cyclohexanol, cyclohexanone, nitrobenzene, methylsalicylate, cumar resin, liquid factice, BRV, which is a product made bythe Barrett Company, and is a liquid high boiling coal tar distillateconsisting chiefly of aromatic hydrocarbons, of specific gravity above1.130 at 38 C. and boiling practically all above 300 0., and parafiux (aproduct of the C. P. Hall Company) which is an especially purifiedresidue obtained in the cracking of petroleum for gasoline and is madeaccording to U. S. Patent No. 1,611,436, granted to Charles P. Hall. Asexamples of the use of such softeners, a mixture of the hard rubbersolution A and the N0. 2 product gave the following results with varioussofteners, the products being used in a ratio of two parts to one and ina concentration of about 10%.

Adding one half part of liquid factice, the composite article gave apull of 58 pounds in the case of a rubber tire carcass stock on iron,and a pull of 88 pounds in the case of a tread stock on iron.

Adding one half part of a 10% solution of of 29 pounds was obtained witha carcass stock and 80 pounds with a tread stock.

Adding one half part of BRV a pull of 97 pounds was obtained with atread stock, while with one part of BRV, a pull of 108 pounds wasobtained and with two parts a pull of 125 pounds.

It has also been found that when both a softener and an organicaccelerator are employed in combination with the mixture of the tworubber solutions, improved results are obtained over the mixture ofrubber solutions alone.

A mixture of the hard rubber solution A, the No. 2 product, BRV, thevulcanization accelerator triethyltrimethylenetriamine combined withstearic acid, and zinc oxide, in the respective v proportions or 10 cc.,5 00., 0.5 gram, 0.05 gram,

and 0.03 gram, gave a pull with a carcass stock of '44 pounds, and witha tread stock of 76 pounds.

A mixture of the same two rubber solutions with aniline and tetramethylthiuram disulphide methyl thiuram disulphide in the same respectiveproportions gave a pull with a carcass stock of 56 pounds and with .atread stock of 102 pounds. The last four examples of the adhesivecompositions also gave excellent results in the lining of barrels andtanks using stocks compounded to cure in exhaust steam and cured in situfor 24 hours; Due to the fact that these stocks contained noreinforcementof fabric, no machine stripping tests were made as thestretching of the rubber renders such tests unreliable.

In any of the described compositions, usual vulcanizing ingredients suchas sulphur and zinc oxide as well as accelerator may be incorporated,and various known vulcanizing procedures may be employed.

As showing that the remarkable results obtained in the bond are due tothe combination of materials comprising the adhesivecompositions and notto the individual ingredients, it is pointed out that where a test wasmade using only the hard rubber solution A, in which the rubber wascombined with 15% or more of sulphur, to bond iron to a carcass stock bycuring for 45 min. at 40 pounds steam pressure in a press, the pull wasonly 0.5 pound, and the same results were obtained with a tread stock.Using separately either of the rubber solutions designated as Nos. 1 and2, under the same conditions, there was obtained a pull of only 3 to 7pounds with a carcass stock and two pounds with a tread stock. Using therubber solution designated as No. 3, the pull was only 7 pounds with acarcass stock and 3 pounds with a tread stock.

The invention provides an adhesive which, while particularly adapted foruniting rubber and rubber-like material to metal, is also capable of usein uniting many other materials. When vulcanized, the bond isnon-thermoplastic up to temperatures at least as high as 120 C.

Thecompositions may also be employed to provide protective coatings onmetal and other articles, said coatings being strongly adherent, andresistant to acids, alkalies, solvents, and chemicals in general. .Insuch cases the coatingmay be hardened by heating in air, steam, orwater, or otherwise, or may remain unvulcanized.

While specific embodiments have been disclosed,..the invention iscapable of modification in many ways, and it is not desired to limit itotherwise. than as required by the prior art.

Having thus described my .invention, what I claim anddesire to protectby Letters Patent, is:

1. A composition comprising; a mixture of products resulting fromfurther vulcanizing one solution of soft vulcanized rubber in thepresence of additional sulphur to at least 15% of chemically combinedsulphur and similarly vulcanizing another such solution to a relativelylow degree of chemically combined sulphur; and an organic softener forrubber.

2. A composition comprising; a mixture of products resulting fromfurther vulcanizing separate solutions of soft vulcanized rubber in thepresence of additional sulphur to widely divergent degrees of combinedsulphur, with the product, of higher combined sulphur contentpredominating and having at least 15% combined sulphur; an organicsoftener for rubber; and an organic accelerator of vulcanization.

3; A composition comprising a mixture of, a solution of rubber of atleast 15% chemically combined sulphur content, a solution of rubber ofabout 4% to 6% chemically combined sulphur content, a solution ofunvulcanized. rubber, an organic softener for rubber, and vulcanizingingredients including an organic accelerator.

4. A composition comprising a rubber solvent,

and in solution therein rubber'chemically eom- 'bined with'at least 15%of sulphur, rubber chemically combined with a relatively 'low percentageof sulphur, unvulcanizedrubber, and vulcanizing ingredients.

5. A homogeneous, fluid composition comprising a mixture of vulcanizedrubber solutions, the rubber of one of which solutions has atleast 15%of chemically combined sulphur, the rubber of another of which solutionshas a relatively low percentage of 'chem'ically'combined sulphur, andvulcanizing ingredients.

6. A composition comprising a mixture of, a solution of soft vulcanizedrubber further vulcanizedin solution in the presence of additionalsulphur'to at least '15 of chemically combined sulphur, and a solutionof soft vulcanized rubber further vulcanized in solution in the presenceof additional sulphur to about 4% to 6% of chemically combinedsulphur..-

7. A composition comprising. a mixture of, a

solution of softyulcanized rubber further vul- 8. A compositioncomprising a rubber solvent,

rubber having a proportion of chemically combined'sulphur equal tothatof hard rubber, rubberhaving a relatively low proportion ofchemically-combined sulphur, unvulcanized rubber, an organic softener.for rubber, and vulcanizing ingredients including an organicaccelerator.

- HARRY L. FISHER.

